1. Field of the Invention
The present invention is in the field of marine propellers, and specifically relates to a hub and propeller assembly made entirely of plastic.
2. The Prior Art
Since the advent of powered ships, marine propellers have traditionally been cast or forged of metal and the hub and blades were formed as a single unitary part. This traditional approach provided strength in the absence of alternative materials, and confidence that the blades would not come loose from the hub.
However, this traditional approach had its inherent disadvantages. The desired strength of the metal blades gave rise to the possibility that if the blade struck a foreign object, enormous forces could be transmitted through the metal blade and hub to the drive shaft, possibly bending it or damaging its mounting.
Because the blades and hub formed a single piece, damage to even one blade required replacement of the entire unit.
Also, if a different pitch were desired, it could only be provided by replacing the entire unit.
As progress in plastic technology developed rapidly after World War II, more than one inventor became interested in the possibility of molding propellers of plastic. The least demanding application appeared to be in electric fans. Typical of these efforts are U.S. Pat. No. 2,811,303 to Ault, et al. and U.S. Pat. No. 4,063,852 to O'Connor. These patents describe molded plastic impellers, and in each case, the blades and hub formed a unitary structure.
As early as 1950, Thompson, J. R. Jr. in U.S. Pat. No. 2,498,348 described a marine propeller of metal-reinforced rubber, which was supposed to reduce fouling of the propeller in weeds.
With further passage of time, plastic manufacturing techniques became more sophisticated as evidenced by U.S. Pat. No. 4,483,214 of Mayer. Mayer describes the production of a spider for a high-speed flywheel, and specifically discusses the use of carbon fibres or glass fibres in an epoxy resin matrix. Even in the spider he describes, the spokes are inseparable from the hub.
In U.S. Pat. No. 4,589,176, Rosman, et al. describe a fiber-composite turbine blade and a method for its construction. The structure of the hub and the manner in which the blade is attached to the hub are not described.
The prior art does not appear to include a practical marine propeller like the present invention.